The present invention relates to wholly aromatic polyesters, particularly wholly aromatic polyesters superior in melt processability and tenacity.
Recently there has been an increasing demand for upgrading of organic, high molecular materials so that there can be obtained fibers, films and moldings superior in mechanical properties such as tensile strength and modulus and in heat resistance.
As a high molecular material which satisfies the above demand there is known a rigid-rod polymer wherein only aromatic rings are linked together in the form of a straight chain. But this polymer is very poor in its solubility to solvents and the melting point thereof is very high. For this reason it has been difficult to effect processing in the state of a solution or in a melted state.
For solving the above problem there have been proposed a method of introducing an aliphatic chain in the main chain, a method of introducing therein an m-substituted compound, a method of introducing therein a 2,6-substituted naphthalene ring, and a method of introducing in an aromatic ring a bulky substituent such as alkyl, halogen, or phenyl. Since the melting point can be lowered by these methods, it becomes possible to effect melt molding, and particularly in a liquid crystal phase, the fluidity is improved and so it becomes easy to perform molding. As typical examples of prior art publications disclosing polymers which exhibit such melt anisotropy there are mentioned Japanese Patent Publications Nos. 47870/1972 and 482/1980, 18016/1981 and 13531/1984 as well as Japanese Patent Laid-Open Nos. 65421/1978, 77691/1979, 144024/1980, 172921/1982, 69199/1979 and 25354/1982.
In those methods, however, there remain many problems to be solved. In the case where an aliphatic chain is copolymerized with the main chain, the resulting polymer is inferior in its mechanical properties and the heat resistance is impaired markedly. Also in the introduction of an m-substituted compound by copolymerization, the mechanical properties of the resulting copolymer are not always satisfactory and the tenacity is impaired. The method of introducing a 2,6-substituted naphthalene ring can afford superior mechanical properties, but the retention of strength at high temperatures is not satisfactory and the monomer is expensive. The method of introducing a bulky substituent is also disadvantageous in that the retention of strength at high temperatures is not satisfactory and the monomer is expensive.
It is the object of the present invention to provide a wholly aromatic polyester capable of being subjected to melt molding and superior in tenacity such as high impact resistance while having superior heat resistance.